I. Field of the Invention
Embodiments of the present invention relate generally to braiding of filaments for use in medical devices and non-medical applications and, more particularly, to a tubular structure and methods for braiding patterns that promote radial strength, collapse resistance, torque transmission, column strength, and kink resistance.
II. Description of the Related Art
Braiding machines have long been used in industry for braiding a variety of filaments, including fibers, thread, yarn, wire, and polymer strands, into tubular structures, such as for use as coverings (e.g., on electric wire) to provide insulation, abrasion resistance and thermal protection. In addition, tubular structures have been used to impart other characteristics, such as radial support (e.g., for high pressure hoses), collapse resistance (e.g., for vacuum tubing), kink resistance, and column strength (e.g., for tubing) and for enhancing other torque transmission properties for various applications.
In the medical device industry, for example, filament braiding has been incorporated into products such as balloon catheters, stents, occlusion devices, vascular grafts, and guide and diagnostic catheters. In particular, tubular structures having a small diameter and incorporating stainless steel, Nickel Titanium (NiTi) alloys, known in the art as Nitinol, and other metallic alloys have been used as coverings, incorporated into a tubular wall, or used as stand-alone medical devices. For example, the use of braided Nitinol alloy wire or certain other alloys exhibiting shape memory characteristics has allowed many devices to be fabricated that can be collapsed for delivery into the body through a catheter and, once deployed from the catheter, can self-expand to a predetermined shape.
In applications such as the delivery of medical devices into remote portions of the human vasculature, the tubular structures should be capable of passing through small diameter vasculature. Thus, the wall thickness and overall profile of the devices becomes increasingly important to the success of the procedure and the comfort of the patient. At the same time, it is desirable for such tubular structures to possess sufficient strength to accomplish certain tasks. For example, tubular structures may be used in stents for the medical treatment of vascular disease to hold open arterial segments that have been narrowed by plaque build up. In some cases, such as with braided Nitinol stents, the stent is stretched to draw down the diameter for delivery through a catheter and self-expands when released from the catheter to abut the arterial wall for supporting the diseased segment. It is thus important that stents have sufficient radial force to hold the artery segment open and resist collapse and kinking, while still being flexible enough to be passed through the delivery catheter through arterial bends without increasing the wire diameter or compromising the functionality of the stent. Similar considerations may also apply to catheter tubing and other tubular structures.
Accordingly, for medical and other applications, there is a need for improved tubular structures that provide increased radial strength, kink resistance, and column strength without necessarily increasing wall thickness in a manner that is simple, cost effective, and overcomes the shortcomings of conventional solutions.